The popularity of running is at an all-time high with nearly
500,000 people in the United States completing a marathon in 2009. (1)
Annual running injury incidence has recently been reported between 19%
and 79%. (2) This large number of injuries has medical providers and
coaches struggling to determine how best to advise their running clients
to prevent injuries. Alternative running styles such as barefoot
running, POSE running, and Chi running have enjoyed an increase in
popularity recently. Proponents of these alternative running styles with
a more anterior landing pattern claim that employing these techniques
will reduce injuries. Little information, however, has been published
comparing the mechanics and injury trends associated with different
running styles.

OVERVIEW OF DIFFERENT RUNNING STYLES

Traditional Shod Running

A recent kinematic analysis of elite runners wearing shoes who
participated in a half marathon indicated that 75% of the runners were
heel strikers, 24% were midfoot strikers, and 1% were forefoot strikers.
(3) When runners use a rearfoot strike pattern, the knee is relatively
extended and the ankle is in relative dorsiflexion upon initial contact.
As the ankle moves into plantarflexion, the knee flexes and the knee
extensors act eccentrically to dampen the ground reaction forces.
Traditionally shod rearfoot strikers often take long strides,
characterized by a vertical displacement of the center of mass and an
impact peak present at approximately 10% to 12% of the stance phase on
the vertical ground reaction force curve (Figure 1). (4) Runners using a
rearfoot strike pattern in bare feet or minimalist footwear have
demonstrated greater initial vertical loading rates than shod heel
strikers. (4,5) Runners using a rearfoot strike may require greater
angular work at the knee (6) resulting in higher patellofemoral and
tibiofemoral compressive forces (7,8) and possibly greater risk of knee
injury than other running styles with more anterior footstrike patterns.
Advocates of barefoot and alternative running styles report that initial
heel contact running is a relatively new phenomenon associated with the
development of the modern running shoes with thicker cushioned heels in
the last 30 to 40 years. Prior to this, many believe the proportion of
midfoot and forefoot strikers was much greater.

Alternative Running Styles

Barefoot running and other alternative running styles have gained
recent popularity, leaving many health care providers with questions
regarding the safety and appropriateness of these techniques for various
running populations. In several publications, barefoot runners exhibited
a more anterior midfoot or forefoot striking pattern, thereby avoiding
heel strike. (4,9-11) A growing number of barefoot running advocates,
teachers, and websites have provided barefoot running instruction since
publication of McDougall's 2009 book. (12) Generally with
habituated barefoot runners, stride length is shortened, stride
frequency is increased, and the vertical displacement of the center of
mass is reduced. (9,13,14)

[FIGURE 1 OMITTED]

One alternative running style that has gained popularity recently
is the POSE method designed by Dr Nicolas Romanov. (15) This running
strategy involves a midfoot to forefoot strike pattern that minimizes
contact time with the support surface and focuses on picking up the feet
and not pushing off the ground as vigorously. (15,16) Romanov claims
that gravity causes the muscle system to absorb body weight on landing
during POSE running, which then produces elastic strain energy. Romanov
further describes that as the center of mass passes over the support
limb, a gravitational torque occurs as extensor muscle activity ceases.
The runner falls forward while the ground reaction forces decrease and
vertical work against gravity is reduced. Romanov suggests that the foot
is unweighted during terminal stance, as it is rapidly pulled from the
ground by hamstring muscle activity to reduce lower-limb inertia and to
catch up with the body. The focus on falling via a gravitational torque
and pulling the foot from the ground effectively differentiates POSE
running from more traditional running forms.

Another alternative running style that has recently gained
popularity is Chi running. The founder of Chi running, Danny Dreyer,
credits the origins of this running form to the discipline of Tai Chi.
(17,18) This method of running is described as the alignment of body,
mind, and forward movement. Runners are instructed to avoid heel strike
and to land with a midfoot strike pattern. The body leans forward
slightly, and the strides are shorter with a focus on relaxed legs.
Dreyer recommends that runners discard more traditional heavily padded
running shoes and use a more minimalist running shoe that involves thin
sole material and limited supportive features. (17,19) In summary,
barefoot, POSE, and Chi runners attempt to land with a midfoot or
forefoot strike, take shorter strides with a greater frequency, and may
demonstrate a reduced initial vertical ground reaction impact compared
with traditional heel-toe shod runners. The original purposes of this
review of literature were to examine additional evidence concerning the
kinematics, kinetics, and injury trends associated with different
running styles. Little to no injury data separated by running styles
were found. Therefore, we discuss the biomechanics of different running
styles and present biomechanical findings associated with different
running injuries.

DATA SOURCES

English language articles published in peer reviewed journals were
identified by searching PubMed, CINAHL, and SPORTDiscus databases. Key
words used in this search included running, barefoot, POSE, Chi,
kinematics, kinetics, injury, and running styles in various
combinations. The authors included original research, meta-analyses, and
review articles in the search. Only one randomized control trial was
identified. (20) Nearly all of the studies included were observational
studies. The search for manuscripts detailing aspects of Chi running in
scientific peer reviewed literature yielded no results. The authors then
resorted to using popular literature and website descriptions of the Chi
running style.

RESULTS

Running Mechanics

Traditional Shod Running

For heel strikers (approximately 80% of shod runners), (3,9) the
initial (impact) peak vertical ground reaction force at heel strike
occurs during the first 10% of stance (21-23) or within approximately 25
milliseconds. (24) This force is passive in nature and the
anterior-posterior component of this impact is generally considered a
braking force with the heel strike anterior to the runner's center
of mass. The second peak for the vertical ground reaction force occurs
between 40% and 50% of the stance phase. (25) This force is more active
as the runner pushes off the ground and the anterior-posterior component
is more propulsive in nature with the runner's center of mass
superior/anterior to the foot contact. Typical running peak vertical
ground reaction forces for runners are between 1.5 and 3.5 times body
weight. (25) Vertical ground reaction forces increase linearly with
increasing running velocity26 and increasing stride length, (27-29) and
decrease with a faster stride rate or cadence. (30) Runners with a
history of injuries may demonstrate greater initial peak vertical ground
reaction forces than healthy matched runners, (22,23,31) however, this
point has been refuted. (32)

Cushioned running shoes are commonly prescribed for runners with
high arches and motion control shoes are often recommended for low
arched runners who require pronation control. Cushioned running shoes
may attenuate the ground reaction force better for high arched runners
(33) and motion control shoes may control instantaneous loading rates
better for low arched runners. (34) Increased resultant joint torques at
the hip and knee have been observed in shod runners compared with
barefoot runners. (7) Aside from the effects of footwear modifications,
some runners may benefit from an altering their running style and
learning to run with a reduced impact load or ground reaction force.
(21) However, this has not been widely studied to date.

Alternative Running Styles

Most habitual barefoot runners choose to land with a midfoot or
forefoot initial foot contact to avoid greater initial loading rates
observed with heel striking in barefeet4 (Figure 1). While most runners
attempting to run in bare feet or minimalist shoes will convert to a
more anterior footstrike, McCarthy et al reported recently on a sample
in which 50% of runners continued to demonstrate a rearfoot strike
pattern 2 weeks after changing to the Vibram 5-finger shoe. (5)

A toe-heel-toe or midfoot contact pattern used by barefoot runners
and other minimalist shoe runners who use this landing strategy may
decrease the vertical loading rates and initial passive peak vertical
ground reaction force by 15% to 33% during the first 25 milliseconds of
foot contact compared to traditional heel-toe strike patterns. (9,35)
This reduction in initial peak vertical ground reaction force is
accomplished by prolonging the time needed to decelerate the
runner's vertical velocity after initial foot contact. By
prolonging this period of time with a greater ankle range of motion,
(10) the vertical ground reaction force is reduced as reflected by the
impulse-momentum equation F=m [DELTA]v/ [DELTA]t, where F=vertical
ground reaction force, m=mass of runner, [DELTA]v=the change in vertical
velocity from initial foot contact to the velocity of zero when downward
motion stops, At=the time required to change the downward velocity to
zero.

The period of time required to change a runner's downward
velocity to zero ([DELTA]t) will likely be longer with a toe-heel-toe
initial contact pattern than with a heel strike pattern. The initial
vertical ground reaction force (F) will therefore be reduced. Another
mechanism to decrease vertical ground reaction forces given a fixed mass
would be to reduce the amount of change in velocity. This can be
accomplished by reducing the vertical height from which the body's
center of mass falls to the ground.36 Essentially, limiting the vertical
displacement of the center of mass prior to foot contact will reduce
[DELTA]v. This is achieved by adopting running styles in which the
runner glides forward more and bounces up and down less.

Little research has been conducted concerning injury trends that
are associated with barefoot or other alternative running styles.
Particularly of concern to some medical providers are metatarsalgia and
other injuries related to foot contact patterns, particularly in bare
feet. (37,38) Injuries caused by excessive contact pressures that are
perpendicular to the foot-ground interface are governed by the equation

contact pressure = contact force/contact area

Wearing minimal footwear that has relatively thin sole material and
no supportive features built into the shoe's construction may
simulate conditions of barefoot running. (39) Running in bare feet or
using minimal footwear may increase peak contact pressure, increase
maximum ground reaction force, and reduce contact area of the foot,
thereby increasing peak pressures imposed on the forefoot. (40,41) For a
given ground reaction force, this reduction in contact area will
significantly increase plantar contact pressure. (40,42,43) A 25% to 63%
reduction in plantar contact area while running in bare feet (44) may
counteract the 15% to 33% reduction in impact peak vertical ground
reaction forces (9,13) achieved from using a toeheel-toe strike pattern.
This could result in potentially greater contact pressures on the more
anterior portions of the metatarsals. High arched runners may experience
greater risk of injurious plantar pressures in the lateral metatarsals,
(45) while low arched runners may experience greater medial and lateral
midfoot contact pressures under a variety of athletic conditions. (46)
Concentrating the center of pressure on the midfoot (47) also increases
the vertical ground reaction impulse stress (force x time) on the
metatarsals. Previous investigators have reported greater stride
frequency with a reduced stride length for individuals who run in bare
feet or for individuals who run using a midfoot or forefoot strike
pattern. (6,14) Greater peak axial strains and strain rates have been
observed in the metatarsals than those in the tibia for barefoot
running. (48) Increased stride frequency has been associated with
reduced knee and hip loading, (36) however the shorter stride length and
increased stride frequency associated with midfoot and forefoot strike
patterns will result in more impacts per unit of time and distance, and
potentially increased cumulative metatarsal strain compared with
rearfoot strike running.

Another potential concern for injury is the increased moment
requirement at the ankle joint associated with a more anterior initial
foot contact. Runners who use a midfoot or forefoot strike pattern will
require greater activation of the plantarflexors during early stance
phase to effect the deceleration and then propulsive impulses. (13) This
muscular activation may lead to increased mechanical work at the ankle
(6,14,49) and additional tensile stress imposed on the plantar flexor
muscles and Achilles tendon. Cole et al observed a greater magnitude and
rate of loading in the ankle joints during the impact phase of barefoot
running compared to shod running. (50)

Supporters of midfoot and forefoot strike running styles blame the
initial peak ground reaction force and loading rate associated with a
rearfoot strike pattern for increased strains that may injure the lower
extremities. (9,31,51) While the initial passive impact peak ground
reaction forces that occur at approximately 10% to 12% stance phase are
greater for shod heel-toe runners, the midstance active propulsive
vertical ground reaction forces may be greater for midfoot or forefoot
strikers (Figure 2). (13,14) These greater active propulsive ground
reaction forces have not yet been correlated with specific injury risk,
but further investigation is warranted.

[FIGURE 2 OMITTED]

Few scientific studies have evaluated the POSE running method.
Dallam observed a decreased stride length, decreased vertical
displacement of the center of mass, and increased oxygen cost when
runners used the POSE method compared with traditional heel-toe running
in a very small sample. (52) Arendse analyzed 20 individual runners who
ran on an outside track, comparing traditional heel-toe running, midfoot
strike running after 15 minutes of instruction, and POSE running after
7.5 hours of instruction. (6) Arendse observed decreased stride length
and decreased vertical displacement of the center of mass when subjects
ran using the POSE method. He reported greater initial vertical ground
reaction forces with heel-toe running. Arendse also observed less
eccentric angular work at the knee joint and greater eccentric angular
work at the ankle joint when subjects ran using the POSE method. This
reduction in angular work at the knee joint is often used to promote use
of the POSE running method. Reducing knee loading at the cost of
increased moment demands at the ankle joint, however, may lead to
increased Achilles tendon or other ankle overuse injuries. Fletcher and
Romanov also observed reduced stance time, decreased vertical and
horizontal displacement of the center of mass, greater knee flexion
angular velocity, and greater stride frequency in a sample of 8 runners
after 7 hours of POSE running instruction.53 Again, this increase in
stride frequency may result in potentially increased cumulative
metatarsal strain and total ankle joint work compared with rearfoot
strike running.

The authors were unable to find any peer-reviewed biomechanical
analyses of Chi running in the literature. In summary, POSE running, Chi
running, barefoot running, and running with a forefoot or midfoot strike
pattern have several commonalities. As shown in the Table, these include
decreased stride length, decreased vertical displacement of the center
of mass, and a possible shift from greater knee joint loading to greater
loading at the ankle joint.

Injury Trends

Annual running injury incidence rates have been reported as ranging
from 19% to 79%,2 with the knee joint being the most commonly injured
anatomic region among runners. (2,54) We were unable to identify any
previous work separating injury trends by running style. With the
majority of modern-day shod runners employing a heel-toe landing style,
(3,9) previous injury reports may relate primarily to this running
style. Potential causes of running related injuries and various
mechanical observations associated with injuries in specific anatomical
regions will be addressed. Finally, we discuss injury trends that may be
related to wearing traditional running shoes or adopting alternative
running styles.

Potential Causes

Many different potential causes have been suggested to explain
running injuries. These potential causative factors can be organized
into extrinsic and intrinsic factors. Extrinsic factors that may be
related to running injury include running shoe age and training errors.
(54,55) Training errors may be more associated with injury incidence
than biomechanical factors. (55) Exposure to a high training load
involving increased intensity, frequency, or running distance (55)
without adequate rest may increase the risk of injury, (56) and
modification of the training schedule may reduce the incidence of
injury. (55-57) The effect of stretching on running injuries has not
been determined. (55,58,59)

Intrinsic causes of injury include a previous history of injury,
(2,54) increased runner age, (54) increased body mass, (54,60) foot
strike characteristics, (23,25,31,61-63) and morphological
characteristics such as excessive genu valgum, (64) pes planus, (31) and
pes cavus feet. (63) Greater instantaneous and average vertical loading
rates have also been observed in runners with a history of injury.
(22,65)

Ankle and Foot Injuries

Particular characteristics present in subjects with a history of
ankle and foot injuries were more years running, weaker plantarflexors,
higher arches, and more inversion at touchdown. (59) McCrory et al
suggest that plantarflexor insufficiency to control the eccentric phase
of dorsiflexion may have contributed to the development of Achilles
tendonopathy. (59) A more rigid foot may lead to "compensatory
overpronation" that overstresses the Achilles tendon. Reduced
tibial external rotation moment and more medial femoral rotation has
also been associated with injury in a group of subjects with a history
of Achilles tendonopathy. (61) Williams et al propose that this places
the lateral gastrocnemius more anteriorly and the medial head of the
gastrocnemius more posteriorly. (61) They hypothesized that this
shortening of the medial head of the gastrocnemius may have resulted in
changes in muscular stress at the musculotendinous junction that may
have lead to the development of Achilles tendonitis. Another possible
explanation may be that increased internal rotation of the entire lower
extremity is associated with increased pronation, which passively
stretches the Achilles tendon.

Increased dorsiflexion range of motion and greater instantaneous
load rates were observed in a population of females with a previous
history of plantar fasciitis. (31) Pohl et al state that the increased
passive dorsiflexion range of motion is usually perceived as desirable.
(31) They attribute this extra motion to the fact that these previously
injured subjects were patients in rehabilitation where they commonly
receive plantar flexor stretching exercises as part of their exercise
prescription. Since this study was retrospective, the authors were
unable to determine if the subjects had the additional range of motion
prior to sustaining an injury or if it was acquired during the time the
subjects spent in rehabilitation. The authors believe that greater
instantaneous rates of loading may subject the plantar fascia to
excessive stress. (31) Two groups of investigators have documented that
greater pronation and leg length inequality were observed in other
samples of plantar fasciitis patients. (63,66) Subotnick previously
reported an association between limb length inequality and greater
pronation. (67) Warren and Jones also observed greater dorsiflexion and
less plantar flexion range of motion in a sample of runners with plantar
fasciitis compared to controls.66 Messier and Pittala observed greater
plantar flexion range of motion in their sample of plantar fasciitis
patients. (63) They hypothesized that excessive sagittal plane motion
may increase the amount of time the runner can impart a propulsive force
which may lead to excessive plantar stresses. (63) These authors also
attribute greater pronation with greater midfoot stress on the plantar
fascia for the injury. (63)

While the balance of running injury literature in the past 30 years
assumes a rearfoot strike pattern while wearing traditional shoes, one
recent case series detailed 2 marathon runners who sustained metatarsal
stress fractures running in barefoot-simulating footwear reportedly
adopting a more anterior footstrike. (38) Another recent military study
reported reduced incidence of tibial and femoral stress fractures as the
body adapted to the increased military training demands of several
cycles of training, but no reduction in metatarsal stress fractures
after months of infantry training. (68) This may suggest that the body
responds differently to metatarsal stress compared to tibial and femoral
stress.

Lower Leg Injuries

Several investigators have examined characteristics of individuals
with lower leg injuries. Heel-toe landing styles have been associated
with greater anterior compartaient pressures than more anterior landing
styles. (69) This could be due to a greater activation of the
dorsiflexors during initial heel contact compared to a midfoot or
forefoot initial contact pattern where greater activation of the
plantarflexors has been observed.13 In a recent case series, 2
previously rearfoot striking patients with chronic exertional
compartment syndrome avoided anterior compartment release surgeries by
adopting a forefoot striking pattern. (70)

Comparing runners with a history of tibial stress fracture to
matched controls, runners with previous tibial stress fractures
exhibited greater peak hip adduction and greater rearfoot eversion
angles during the stance phase of running. (62,71) Milner and Pohl
hypothesized that these forces may have induced a tensile stress on the
posteromedial aspect of the tibia. (62,71) These authors also observed
greater absolute free moment for individuals who had incurred previous
tibial stress fractures. (51,62) Absolute free moment was defined as the
torque acting between the foot and the ground at impact which may impose
a torsional stress on the tibia. (62) Similarly, greater pronation and
velocity of pronation were observed in subjects with a history of shin
splints. (63) This increased pronation may increase the stress on the
posterior medial tibia as increased stretching of the tibialis posterior
imposes greater tensile stress on its proximal attachment site. Greater
anterior-posterior braking force and vertical ground reaction forces
were observed in another sample of tibial stress fracture patients. (72)
Zifchock et al suggest that high peak tibial shock may lead to injury.
(72) Creaby and Dixon, however, recently reported no differences in the
magnitude of free moment, sagittal, or frontal plane vertical ground
reaction forces observed in a small sample of military members with
tibial stress fracture compared to matched controls. (32) In a recent
systematic review, (73) Zadpoor and Nikooyan contend that greater
vertical loading rates and not greater vertical ground reaction forces
are more often associated with lower extremity stress fractures.
(22,72,74,75) Additionally, no significant intrinsic risk factors were
identified in a population of collegiate runners with exercise related
leg pain. (76)

In a sample of military recruits, Cowan observed higher odds ratios
for lower extremity overuse injuries in soldiers with the highest
arches. (84) Messier also observed a similar trend with recreational
athletes. (63) Higher arches were associated with greater lower
extremity injury incidence in a different sample of female athletes.
(85) Higher arches may be associated with rigid feet that do not promote
shock absorption at initial foot contact. In a sample of 20 high arched
runners, Williams et al observed more bony injuries and lateral injuries
in the lower extremities (ie, 5th metatarsal stress fractures, lateral
ankle sprains, and iliotibial band syndrome). (86) They also detected
more medial injuries, knee injuries, and soft tissue injuries in a
sample of 20 low arched runners. (86)

Traditional Running Shoes

In an effort to correct undesirable and possibly injurious
mechanics, many healthcare professionals prescribe running shoes with
extra cushioning to provide shock absorption, or motion control
characteristics to limit pronation. (33,34) Cushioned running shoes may
increase contact area and reduce contact pressures in cavus feet.
(44,87) Likewise, motion control shoes may increase plantar contact
area, reduce tibial internal rotation, and reduce plantar contact
pressures in runners with flatter feet. (33,44) Recently, the practice
of matching foot morphology to running shoe type has been questioned.
(20,88,89) Even though undesirable mechanics have been prevented in
laboratory settings by specific shoe selection and modification, no
well-designed studies have demonstrated significant injury reduction by
using this commonly used practice of shoe prescription. In the last
decade, the results of several studies have demonstrated a correlation
between injury and loading rates, and between injury and impact forces.
(22,23,31) This growing body of evidence suggests that runners who have
developed strike patterns that incorporate relatively low levels of
impact forces and a more moderate rate of pronation are at a reduced
risk of incurring overuse running injuries. (22,23,31)

Alternative Running Styles

Little to no research exists for injury patterns that may be
associated with POSE, Chi, or barefoot running styles. Danny Dreyer
claims that the braking forces of heel strike are responsible for many
lower extremity overuse injuries. (17-19) The authors could not find any
scientific manuscripts in any peer-reviewed journals to substantiate
claims that Chi running is safer or superior to traditional heel-toe
running mechanics in injury prevention or running economy. Dr Mark
Cucuzella presented survey findings of 2500 Chi runners in 2008.
Approximately 90% of the runners had favorable impressions of Chi
running. Unfortunately, this survey was originally made available to
approximately 25,000 people who had purchased Chi running materials and
only 10% responded. Theoretically, the adoption of these alternative
running styles may shift stress from the knee joint to the ankle joint,
(6,8,50) potentially resulting in ankle and foot related injuries. These
alternative running forms may be desirable if a runner has a history of
knee injuries or knee osteoarthritis and is attempting to shift stress
away from the knee joint. More research is needed to compare the
mechanics of various running styles and to survey runners who have
adopted these running styles for a sufficient period of time to assess
the type and severity of injuries they are experiencing.

SUMMARY

Clinicians are often faced with questions from patients about
running shoe selection and running style. Traditional shod heel-toe
strike running gait has been challenged recently by individuals who
advocate a more anterior initial foot contact, or minimal to no footwear
which tends to force runners to make initial contact more anteriorly on
the foot. Decreasing or eliminating the initial vertical ground reaction
peak or "impact transient" has been cited as a potential
method to reduce knee joint injuries or injuries in other anatomic
regions. This theory requires further investigation to prove its injury
prevention claims and to insure that runners who adopt a more anterior
strike pattern are not merely increasing their risk for foot and ankle
injuries.

Certainly more research is needed to determine ultimately which
individuals with certain morphological or mechanical gait
characteristics may benefit from alternative running styles that
incorporate a more anterior initial foot contact with or without shoes.
Controlled longitudinal studies are needed to assess the utility of
adopting alternative running styles in an effort to reduce injury rates.
Laboratory research comparing the mechanics of various running styles is
needed to quantify internal force and moment demands of the various
joints in multiple planes. Additional running shoe research is required
with large samples of experienced runners to examine the potential
effectiveness of matching running shoes to running mechanics and not
merely foot morphology. Unbiased injury history surveys are also needed
to evaluate the incidence of injury associated with various running
styles.

(61.) Williams DS, Zambardino JA, Banning VA. Transverse-plane
mechanics at the knee and tibia in runners with and without a history of
achilles tendonopathy. J Orthop Sports Phys Ther. 2008;38(12):761-767.